Address resolution protocol system and method in a virtual network

ABSTRACT

A virtual networking system and method are disclosed. Switched Ethernet local area network semantics are provided over an underlying point to point mesh. Computer processor nodes may directly communicate via virtual interfaces over a switch fabric or they may communicate via an ethernet switch emulation. Address resolution protocol logic helps associate IP addresses with virtual interfaces while allowing computer processors to reply to ARP requests with virtual MAC addresses.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. provisional application Ser.No. 60/285,296, filed on Apr. 20, 2001, which is hereby incorporated byreference.

BACKGROUND

1. Field of the Invention

The present invention relates to computing systems for enterprises andapplication service providers and, more specifically, to processingsystems having virtualized communication networks.

2. Discussion of Related Art

In current enterprise computing and application service providerenvironments, personnel from multiple information technology (IT)functions (electrical, networking, etc.) must participate to deployprocessing and networking resources. Consequently, because of schedulingand other difficulties in coordinating activities from multipledepartments, it can take weeks or months to deploy a new computerserver. This lengthy, manual process increases both human and equipmentcosts, and delays the launch of applications.

Moreover, because it is difficult to anticipate how much processingpower applications will require, managers typically over-provision theamount of computational power. As a result, data-center computingresources often go unutilized or under-utilized.

If more processing power is eventually needed than originallyprovisioned, the various IT functions will again need to coordinateactivities to deploy more or improved servers, connect them to thecommunication and storage networks and so forth. This task getsincreasingly difficult as the systems become larger.

Deployment is also problematic. For example, when deploying 24conventional servers, more than 100 discrete connections may be requiredto configure the overall system. Managing these cables is an ongoingchallenge, and each represents a failure point. Attempting to mitigatethe risk of failure by adding redundancy can double the cabling,exacerbating the problem while increasing complexity and costs.

Provisioning for high availability with today's technology is adifficult and costly proposition. Generally, a failover server must bedeployed for every primary server. In addition, complex managementsoftware and professional services are usually required.

Generally, it is not possible to adjust the processing power or upgradethe CPUs on a legacy server. Instead, scaling processor capacity and/ormigrating to a vendor's next-generation architecture often requires a“forklift upgrade,” meaning more hardware/software systems are added,needing new connections and the like.

Consequently, there is a need for a system and method of providing aplatform for enterprise and ASP computing that addresses the aboveshortcomings.

SUMMARY

The present invention features a platform and method for computerprocessing in which virtual processing area networks may be configuredand deployed.

According to one aspect of the invention, a method and system ofimplementing an address resolution protocol (ARP) are provided. Acomputing platform has a plurality of processors connected by anunderlying physical network. Logic, executable on one of the processors,defines a topology of an Ethernet network to be emulated on thecomputing platform. The topology includes processor nodes and a switchnode. Logic, executable on one of the processors, assigns a set ofprocessors from the plurality to be processors to act as the processornodes. Logic, executable on one of the processors, assigns virtual MACaddresses to each processor node of the emulated Ethernet network.Logic, executable on one of the processors, allocates virtual interfacesover the underlying physical network to provide direct softwarecommunication from each processor node to each other processor node.Each virtual interface has a corresponding identification. Eachprocessor node has ARP request logic to communicate an ARP request tothe switch node, in which the ARP request includes an IP address. Theswitch node includes ARP request broadcast logic to communicate the ARPrequest to all other processor nodes in the emulated Ethernet network.Each processor node has ARP reply logic to determine whether it is theprocessor node associated with the IP address in an ARP request and, ifso, to issue to the switch node an ARP reply, wherein the ARP replycontains the virtual MAC address of the processor node associated withthe IP address. The switch node includes ARP reply logic to receive theARP reply and to modify the ARP reply to include to include a virtualinterface identification for the ARP requesting node.

BRIEF DESCRIPTION OF THE DRAWINGS

In the Drawing,

FIG. 1 is a system diagram illustrating one embodiment of the invention;

FIGS. 2A–C are diagrams illustrating the communication links establishedaccording to one embodiment of the invention;

FIGS. 3A–B are diagrams illustrating the networking softwarearchitecture of certain embodiments of the invention;

FIGS. 4A–C are flowcharts illustrating driver logic according to certainembodiments of the invention;

FIG. 5 illustrates service clusters according to certain embodiments ofthe invention;

FIG. 6 illustrates the storage software architecture of certainembodiments of the invention;

FIG. 7 illustrates the processor-side storage logic of certainembodiments of the invention;

FIG. 8 illustrates the storage address mapping logic of certainembodiments of the invention; and

FIG. 9 illustrates the cluster management logic of certain embodimentsof the invention.

DETAILED DESCRIPTION

Preferred embodiments of the invention provide a processing platformfrom which virtual systems may be deployed through configurationcommands. The platform provides a large pool of processors from which asubset may be selected and configured through software commands to forma virtualized network of computers (“processing area network” or“processor clusters”) that may be deployed to serve a given set ofapplications or customer. The virtualized processing area network (PAN)may then be used to execute customer specific applications, such asweb-based server applications. The virtualization may includevirtualization of local area networks (LANs) or the virtualization ofI/O storage. By providing such a platform, processing resources may bedeployed rapidly and easily through software via configuration commands,e.g., from an administrator, rather than through physically providingservers, cabling network and storage connections, providing power toeach server and so forth.

Overview of the Platform and its Behavior

As shown in FIG. 1, a preferred hardware platform 100 includes a set ofprocessing nodes 105 a–n connected to a switch fabrics 115 a,b viahigh-speed, interconnect 110 a,b. The switch fabric 115 a,b is alsoconnected to at least one control node 120 a,b that is in communicationwith an external IP network 125 (or other data communication network),and with a storage area network (SAN) 130. A management application 135,for example, executing remotely, may access one or more of the controlnodes via the IP network 125 to assist in configuring the platform 100and deploying virtualized PANs.

Under certain embodiments, about 24 processing nodes 105 a–n, twocontrol nodes 120, and two switch fabrics 115 a,b are contained in asingle chassis and interconnected with a fixed, pre-wired mesh ofpoint-to-point (PtP) links. Each processing node 105 is a board thatincludes one or more (e.g., 4) processors 106 j–l, one or more networkinterface cards (NICs) 107, and local memory (e.g., greater than 4Gbytes) that, among other things, includes some BIOS firmware forbooting and initialization. There is no local disk for the processors106; instead all storage, including storage needed for paging, ishandled by SAN storage devices 130.

Each control node 120 is a single board that includes one or more (e.g.,4) processors, local memory, and local disk storage for holdingindependent copies of the boot image and initial file system that isused to boot operating system software for the processing nodes 105 andfor the control nodes 106. Each control node communicates with SAN 130via 100 megabyte/second fibre channel adapter cards 128 connected tofibre channel links 122, 124 and communicates with the Internet (or anyother external network) 125 via an external network interface 129 havingone or more Gigabit Ethernet NICs connected to Gigabit Ethernet links121,123. (Many other techniques and hardware may be used for SAN andexternal network connectivity.) Each control node includes a low speedEthernet port (not shown) as a dedicated management port, which may beused instead of remote, web-based management via management application135.

The switch fabrics is composed of one or more 30-port Giganet switches115, such as the NIC-CLAN 1000 and clan 5300 switch, and the variousprocessing and control nodes use corresponding NICs for communicationwith such a fabric module. Giganet switch fabrics have the semantics ofa Non-Broadcast Multiple Access (NBMA) network. All inter-nodecommunication is via a switch fabric. Each link is formed as a serialconnection between a NIC 107 and a port in the switch fabric 115. Eachlink operates at 112 megabytes/second.

In some embodiments, multiple cabinets or chassises may be connectedtogether to form larger platforms. And in other embodiments theconfiguration may differ; for example, redundant connections, switchesand control nodes may be eliminated.

Under software control, the platform supports multiple, simultaneous andindependent processing areas networks (PANs). Each PAN, through softwarecommands, is configured to have a corresponding subset of processors 106that may communicate via a virtual local area network that is emulatedover the PtP mesh. Each PAN is also configured to have a correspondingvirtual I/O subsystem. No physical deployment or cabling is needed toestablish a PAN. Under certain preferred embodiments, software logicexecuting on the processor nodes and/or the control nodes emulatesswitched Ethernet semantics; other software logic executing on theprocessor nodes and/or the control nodes provides virtual storagesubsystem functionality that follows SCSI semantics and that providesindependent I/O address spaces for each PAN.

Network Architecture

Certain preferred embodiments allow an administrator to build virtual,emulated LANs using virtual components, interfaces, and connections.Each of the virtual LANs can be internal and private to the platform100, or multiple processors may be formed into a processor clusterexternally visible as a single IP address.

Under certain embodiments, the virtual networks so created emulate aswitched Ethernet network, though the physical, underlying network is aPtP mesh. The virtual network utilizes IEEE MAC addresses, and theprocessing nodes support IETF ARP processing to identify and associateIP addresses with MAC addresses. Consequently, a given processor nodereplies to an ARP request consistently whether the ARP request came froma node internal or external to the platform.

FIG. 2A shows an exemplary network arrangement that may be modeled oremulated. A first subnet 202 is formed by processing nodes PN₁, PN₂, andPN_(k) that may communicate with one another via switch 206. A secondsubnet 204 is formed by processing nodes PN_(k) and PN_(m) that maycommunicate with one another via switch 208. Under switched Ethernetsemantics, one node on a subnet may communicate directly with anothernode on the subnet; for example, PN₁ may send a message to PN₂. Thesemantics also allow one node to communicate with a set of the othernodes; for example PN₁ may send a broadcast message to other nodes. Theprocessing nodes PN₁ and PN₂ cannot directly communicate with PN_(m)because PN_(m) is on a different subnet. For PN₁ and PN₂ to communicatewith PN_(m) higher layer networking software would need to be utilized,which software would have a fuller understanding of both subnets. Thoughnot shown in the figure, a given switch may communicate via an “uplink”to another switch or the like. As will be appreciated given thedescription below, the need for such uplinks is different than theirneed when the switches are physical. Specifically, since the switchesare virtual and modeled in software they may scale horizontally as wideas needed. (In contrast, physical switches have a fixed number ofphysical ports sometimes the uplinks are needed to provide horizontalscalability.)

FIG. 2B shows exemplary software communication paths and logic usedunder certain embodiments to model the subnets 202 and 204 of FIG. 2A.The communication paths 212 connect processing nodes PN₁, PN₂, PN_(k),and PN_(m), specifically their corresponding processor-side networkcommunication logic 210, and they also connect processing nodes tocontrol nodes. (Though drawn as a single instance of logic for thepurpose of clarity, PN_(k) may have multiple instances of thecorresponding processor logic, one per subnet, for example.) Underpreferred embodiments, management logic and the control node logic areresponsible for establishing, managing and destroying the communicationpaths. The individual processing nodes are not permitted to establishsuch paths.

As will be explained in detail below, the processor logic and thecontrol node logic together emulate switched Ethernet semantics oversuch communication paths. For example, the control nodes have controlnode-side virtual switch logic 214 to emulate some (but not necessarilyall) of the semantics of an Ethernet switch, and the processor logicincludes logic to emulate some (but not necessarily all) of thesemantics of an Ethernet driver.

Within a subnet, one processor node may communicate directly withanother via a corresponding virtual interface 212. Likewise, a processornode may communicate with the control node logic via a separate virtualinterface. Under certain embodiments, the underlying switch fabric andassociated logic (e.g., switch fabric manager logic, not shown) providesthe ability to establish and manage such virtual interfaces (VIs) overthe point to point mesh. Moreover, these virtual interfaces may beestablished in a reliable, redundant fashion and are referred to hereinin as RVIs. At points in this description, the terms virtual interface(VI) and reliable virtual interface (RVI) are used interchangeably, asthe choice between a VI versus an RVI largely depends on the amount ofreliability desired by the system at the expense of system resources.

Referring conjointly to FIGS. 2A–B, if node PN₁ is to communicate withnode PN₂ it does so ordinarily by virtual interface 212 ₁₋₂. However,preferred embodiments allow communication between PN₁ and PN₂ to occurvia switch emulation logic, if for example VI 212 ₁₋₂ is not operatingsatisfactorily. In this case a message may be sent via VI 212_(1-switch206) and via VI 212 _(switch206-2). If PN₁ is to broadcast ormulticast a message to other nodes in the subnet 202 it does so bysending the message to control node-side logic 214 via virtual interface212 _(1-switch206). Control node-side logic 214 then emulates thebroadcast or multicast functionality by cloning and sending the messageto the other relevant nodes using the relevant VIs. The same oranalogous VIs may be used to convey other messages requiring controlnode-side logic. For example, as will be described below, controlnode-side logic includes logic to support the address resolutionprotocol (ARP), and VIs are used to communicate ARP replies and requeststo the control node. Though the above description suggests just one VIbetween processor logic and control logic, many embodiments employseveral such connections. Moreover, though the figures suggest symmetryin the software communication paths, the architecture actually allowsasymmetric communication. For example, as will be discussed below, forcommunication clustered services the packets would be routed via thecontrol node. However, return communication may be direct between nodes.

Notice that like the network of FIG. 2A, there is no mechanism forcommunication between node PN₂, and PN_(m). Moreover, by havingcommunication paths managed and created centrally (instead of via theprocessing nodes) such a path is not creatable by the processing nodes,and the defined subnet connectivity cannot be violated by a processor.

FIG. 2C shows the exemplary physical connections of certain embodimentsto realize the subnets of FIGS. 2A and B. Specifically, each instance ofprocessing network logic 210 communicates with the switch fabric 115 viaa PtP links 216 of interconnect 110. Likewise, the control node hasmultiple instances of switch logic 214 and each communicates over a PtPconneciton 216 to the switch fabric. The virtual interfaces of FIG. 2Binclude the logic to convey information over these physical links, aswill be described further below.

To create and configure such networks, an administrator defines thenetwork topology of a PAN and specifies (e.g., via a utility within themanagement software 135) MAC address assignments of the various nodes.The MAC address is virtual, identifying a virtual interface, and nottied to any specific physical node. Under certain embodiments, MACaddresses follow the IEEE 48 bit address format, but in which thecontents include a “locally administered” bit (set to 1), the serialnumber of the control node 120 on which the virtual interface wasoriginally defined (more below), and a count value from a persistentsequence counter on the control node that is kept in NVRAM in thecontrol node. These MACs will be used to identify the nodes (as isconventional) at a layer 2 level. For example, in replying to ARPrequests (whether from a node internal to the PAN or on an externalnetwork) these MACs will be included in the ARP reply.

The control node-side networking logic maintains data structures thatcontain information reflecting the connectivity of the LAN (e.g., whichnodes may communicate to which other nodes). The control node logic alsoallocates and assigns VI (or RVI) mappings to the defined MAC addressesand allocates and assigns VIs or (RVIs) between the control nodes andbetween the control nodes and the processing nodes. In the example ofFIG. 2A, the logic would allocate and assign VIs 212 of FIG. 2B. (Thenaming of the VIs and RVIs in some embodiments is a consequence of theswitching fabric and the switch fabric manager logic employed.)

As each processor boots, BIOS-based boot logic initializes eachprocessor 106 of the node 105 and, among other things, establishes a (ordiscovers the) VI 212 to the control node logic. The processor node thenobtains from the control node relevant data link information, such asthe processor node's MAC address, and the MAC identities of otherdevices within the same data link configuration. Each processor thenregisters its IP address with the control node, which then binds the IPaddress to the node and an RVI (e.g., the RVI on which the registrationarrived). In this fashion, the control node will be able to bind IPaddresses for each virtual MAC for each node on a subnet. In addition tothe above, the processor node also obtains the RVI or VI-relatedinformation for its connections to other nodes or to control nodenetworking logic.

Thus, after boot and initialization, the various processor nodes shouldunderstand their layer 2, data link connectivity. As will be explainedbelow, layer 3 (IP) connectivity and specifically layer 3 to layer 2associations are determined during normal processing of the processorsas a consequence of the address resolution protocol.

FIG. 3A details the processor-side networking logic 210 and FIG. 3Bdetails the control node-side networking 310 logic of certainembodiments. The processor side logic 210 includes IP stack 305, virtualnetwork driver 310, ARP logic 350, RCLAN layer 315, and redundantGiganet drivers 320 a,b. The control node-side logic 310 includesredundant Giganet drivers 325 a,b, RCLAN layer 330, virtual Clusterproxy logic 360, virtual LAN server 335, ARP server logic 355, virtualLAN proxy 340, and physical LAN drivers 345.

IP Stack

The IP stack 305 is the communication protocol stack provided with theoperating system (e.g., Linux) used by the processing nodes 106. The IPstack provides a layer 3 interface for the applications and operatingsystem executing on a processor 106 to communicate with the simulatedEthernet network. The IP stack provides packets of information to thevirtual Ethernet layer 310 in conjunction with providing a layer 3, IPaddress as a destination for that packet. The IP stack logic isconventional except that certain embodiment avoid check sum calculationsand logic.

Virtual Ethernet Driver

The virtual Ethernet driver 310 will appear to the IP stack 305 like a“real” Ethernet driver. In this regard, the virtual Ethernet driver 310receives IP packets or datagrams from the IP stack for subsequenttransmission on the network, and it receives packet information from thenetwork to be delivered to the stack as an IP packet.

The stack builds the MAC header. The “normal” Ethernet code in the stackmay be used. The virtual Ethernet driver receives the packet with theMAC header already built and the correct MAC address already in theheader.

In material part and with reference to FIGS. 4A–C, the virtual Ethernetdriver 310 dequeues 405 outgoing IP datagrams so that the packet may besent on the network. The standard IP stack ARP logic is used. Thedriver, as will be explained below, intercepts all ARP packets enteringand leaving the system to modify them so that the proper informationends up in each node's ARP tables. The normal ARP logic places thecorrect MAC address in the link layer header of the outgoing packetbefore the packet is queued to the Ethernet driver. The driver then justexamines the link layer header and destination MAC to determine how tosend the packet. The driver does not directly manipulate the ARP table(except for the occasional invalidation of ARP entries).

The driver 310 determines 415 whether ARP logic 350 has MAC addressinformation (more below) associated with the IP address in the dequeuedpacket. If the ARP logic 350 has the information, the information isused to send 420 the packet accordingly. If the ARP logic 350 does nothave the information, the driver needs to determine such information,and in certain preferred embodiments, this information is obtained as aresult of an implementation of the ARP protocol as discussed inconnection with FIGS. 4B–C.

If the ARP logic 350 has the MAC address information, the driveranalyzes the information returned from the ARP logic 350 to determinewhere and how to send the packet. Specifically, the driver looks at theaddress to determine whether the MAC address is in a valid format or ina particular invalid format. For example, in one embodiment, internalnodes (i.e., PAN nodes internal to the platform) are signaled through acombination of setting the locally administered bit, the multicast bit,and another predefined bit pattern in the first byte of the MAC address.The overarching pattern is one which is highly improbable of being avalid pattern.

If the MAC address returned from the ARP logic is in a valid format, theIP address associated with that MAC address is for a node external atleast to the relevant subnet and in preferred embodiments is external tothe platform. To deliver such a packet, the driver prepends the packetwith a TLV (type-length-value) header. The logic then sends the packetto the control node over a pre-established VI. The control node thenhandles the rest of the transmission as appropriate.

If the MAC address information returned from the ARP logic 350 is in ana particular invalid format, the invalid format signals that theIP-addressed node is to an internal node, and the information in the MACaddress information is used to help identify the VI (or RVI) directlyconnecting the two processing nodes. For example, the ARP table entrymay hold information identifying the RVI 212 to use to send the packet,e.g., 212 ₁₋₂, to another processing node. The driver prepends thepacket with a TLV header. It then places address information into theheader as well as information identifying the Ethernet protocol type.The logic then selects the appropriate VI (or RVI) on which to send theencapsulated packet. If that VI (or RVI) is operating satisfactorily itis used to carry the packet; if it is operating unsatisfactorily thepacket is sent to the control node switch logic (more below) so that theswitch logic can send it to the appropriate node. Though the ARP tablemay contain information to actually specify the RVI to use, many othertechniques may be employed. For example, the information in the tablemay indirectly provide such information, e.g., by pointing to theinformation of interest or otherwise identifying the information ofinterest though not contain it.

For any multicast or broadcast type messages, the driver sends themessage to the control node on a defined VI. The control node thenclones the packet and sends it to all nodes (excluding the sending node)and the uplink accordingly.

If there is no ARP mapping then the upper layers would never have sentthe packet to the driver. If there is no datalink layer mappingavailable, the packet is put aside until ARP resolution is completed.Once the ARP layer has finished ARPing, the packets held back pendingARP get their datalink headers build and the packets are then sent tothe driver.

If the ARP logic has no mapping for an IP address of an IP packet fromthe IP stack and, consequently, the driver 310 is unable to determinethe associated addressing information (i.e., MAC address or RVI-relatedinformation), the driver obtains such information by following the ARPprotocol. Referring to FIGS. 4B–C, the driver builds 425 an ARP requestpacket containing the relevant IP address for which there is no MACmapping in the local ARP table. The node then prepends 430 the ARPpacket with a TLV-type header. The ARP request is then sent via adedicated RVI to the control node-side networking logic—specifically,the virtual LAN server 335.

As will be discussed in more detail below, the ARP request packet isprocessed 435 by the control node and broadcast 440 to the relevantnodes. For example, the control node will flag whether the requestingnode is part of an IP service cluster.

The Ethernet driver logic 310 at the relevant nodes receives 445 the ARPreply, and determines 450 if it is the target of the ARP request bycomparing the target IP address with a list of locally configured IPaddresses by making calls to the node's IP stack. If it is not thetarget, it passes up the packet without modification. If it is thetarget, the driver creates 460 a local MAC header from the TLV headerand updates 465 the local ARP table and creates an ARP reply. The drivermodifies the information in the ARP request (mainly the source MAC) andthen passes the ARP request up normally for the upper layers to handle.It is the upper layers that form the ARP reply when necessary. The replyamong other things contains the MAC address of the replying node and hasa bit set in the TLV header indicating that the reply is from a localnode. In this regard, the node responds according to IETF-type ARPsemantics (in contrast to ATM ARP protocols in which ARP replies arehandled centrally). The reply is then sent 470.

As will be explained in more detail below, the control node logic 335receives 473 the reply and modifies it. For example, the control nodemay substitute the MAC address of a replying, internal node withinformation identifying the source cabinet, processing node number, RVIconnection number, channel, virtual interface number, and virtual LANname. Once the ARP reply is modified the control node logic then sends475 the ARP reply to an appropriate node, i.e., the node that sent theARP request, or in specific instances to the load balancer in an IPservice cluster, discussed below.

Eventually, an encapsulated ARP reply is received 480. If the replyingnode is an external node, the ARP reply contains the MAC address of thereplying node. If the replying node is an internal node, the ARP replyinstead contains information identifying the relevant RVI to communicatewith the node. In either case, the local table is updated 485.

The pending datagram is dequeued 487, and the appropriate RVI isselected 493. As discussed above, the appropriate RVI is selected basedon whether the target node is internal or external. A TLV header isprepended to the packet and sent 495.

For communications within a virtual LAN the maximum transmission unit(MTU) is configured as 16896 bytes. Even though the configured MTU is16896 bytes, the Ethernet driver 310 recognizes when a packet is beingsent to an external network. Through the use of path MTU discovery, ICMPand IP stack changes, the path MTU is changed at the source node 105.This mechanism is also used to trigger packet check summing.

Certain embodiments of the invention support promiscuous mode through acombination of logic at the virtual LAN server 335 and in the virtualLAN drivers 310. When a virtual LAN driver 310 receives a promiscuousmode message from the virtual LAN server 335, the message containsinformation about the identity of the receiver desiring to enterpromiscuous mode. This information includes the receiver's location(cabinet, node, etc), the interface number of the promiscuous virtualinterface 310 on the receiver (required for demultiplexing packets), andthe name of the virtual LAN to which the receiver belongs. Thisinformation is then used by the driver 310 to determine how to sendpromiscuous packets to the receiver (which RVI or other mechanism to useto send the packets). The virtual interface 310 maintains a list ofpromiscuous listeners on the same virtual LAN. When a sending nodereceives a promiscuous mode message it will update its promiscuous listaccordingly.

When a packet is transmitted over a virtual Ethernet driver 310, thislist will be examined. If the list is not empty, then the virtualEthernet interface 310 will do the following:

-   -   If the outgoing packet is being broadcast or multicast, no        promiscuous copy will be sent. The normal broadcast operation        will transmit the packet to the promiscuous listener(s)    -   If the packet is a unicast packet with a destination other than        the promiscuous listener, the packet will be cloned and sent to        the promiscuous listeners.

The header TLV includes extra information the destination can use todemultiplex and validate the incoming packet. Part of this informationis the destination virtual Ethernet interface number (destination devicenumber on the receiving node). Since these can be different between theactual packet destination and the promiscuous destination, this headercannot simply be cloned. Thus, memory will have to be allocated for eachheader for each packet clone to each promiscuous listener. When thepacket header for a promiscuous packet is built the packet type will beset to indicate that the packet was a promiscuous transmission ratherthan a unicast transmission.

The virtual Ethernet driver 310 is also responsible for handling theredundant control node connections. For example, the virtual Ethernetdrivers will periodically test end-to-end connectivity by sending aheartbeat TLV to each connected RVI. This will allow virtual Ethernetdrivers to determine if a node has stopped responding or whether astopped node has started to respond again. When an RVI or control node120 is determined to be down, the Ethernet driver will send trafficthrough the surviving control node. If both control nodes are functionalthe driver 310 will attempt to load balance traffic between the twonodes.

Certain embodiments of the invention provide performance improvements.For example, with modifications to the IP stack 305, packets sent onlywithin the platform 100 are not check summed since all elements of theplatform 100 provide error detection and guaranteed data delivery.

In addition, for communications within a PAN (or even within a platform100) the RVI may be configured so that the packets may be larger thanthe maximum size permitted by Ethernet. Thus, while the model emulatesEthernet behavior in certain embodiments maximum packet size may beviolated to improve performance. The actual packet size will benegotiated as part of the data link layer.

Failure of a control node is detected either by a notification from theRCLAN layer, or by a failure of heartbeat TLVs. If a control node failsthe Ethernet driver 310 will send traffic only to the remaining controlnode. The Ethernet driver 310 will recognize the recovery of a controlnode via notification from the RCLAN layer or the resumption ofheartbeat TLVs. Once a control node has recovered, the Ethernet driver310 will resume load balancing.

If a node detects that it cannot communicate with another node via adirect RVI (as outlined above) the node attempts to communicate via thecontrol node, acting as a switch. Such failure may be signaled by thelower RCLAN layer, for example from failure to receive a virtualinterface acknowledgement or from failures detected through heartbeatmechanisms. In this instance, the driver marks bits in the TLV headeraccordingly to indicate that the message is to be unicast and sends thepacket to the control node so that it can send the packet to the desirednode (e.g., based on the IP address, if necessary).

RCLAN Layer

The RCLAN layer 315 is responsible for handling the redundancy,fail-over and load balancing logic of the redundant interconnect NICs107. This includes detecting failures, re-routing traffic over aredundant connection on failures, load balancing, and reportinginability to deliver traffic back to the virtual network drivers 310.The virtual ethernet drivers 310 expect to be notified asynchronouslywhen there is a fatal error on any RVI that makes the RVI unusable or ifany RVI is taken down for any reason.

Under normal circumstances the virtual network driver 310 on eachprocessor will attempt to load balance outgoing packets betweenavailable control nodes. This can be done via simple round-robinalternation between available control nodes, or by keeping track of howmany bytes have been transmitted on each and always transmitting on thecontrol nodes through which fewest bytes have been sent.

The RCLAN provides high bandwidth (224 MB/sec each way) low latencyreliable asynchronous point-to-point communication between kernels. Thesender of the data is notified if the data cannot be delivered and abest effort will be made to deliver it. The RCLAN uses two Giganet clan1000 cards to provide redundant communication paths between kernels. Itseamlessly recovers single failures in the clan 1000 cards or theGiganet switches. It detects lost data and data errors and resends thedata if needed. Communication will not be disrupted as long as one ofthe connections is partially working, e.g., the error rate does notexceed 5%. Clients of the RCLAN include the RPC mechanism, the remoteSCSI mechanism, and remote Ethernet. The RCLAN also provide a simpleform of flow control. Low latency and high concurrency are achieved byallowing multiple simultaneous requests for each device to be sent bythe processor node to the control node, so that they can be forwarded tothe device as soon as possible or, alternatively so that they can bequeued for completion as close to the device as possible as opposed toqueuing all requests on the processor node.

The RCLAN layer 330 on the control node-side operates analogously to theabove.

Giganet Driver

The Giganet driver logic 320 is the logic responsible for providing aninterface to the Giganet NIC 107, whether on a processor 106 or controlnode 120. In short, the Giganet driver logic establishes VI connections,associated by VI id's, so that the higher layers, e.g., RCLAN 315 andEthernet driver 310, need only understand the semantics of VI's.

Giganet driver logic 320 is responsible for allocating memory in eachnode for buffers and queues for the VI's, and for conditioning the NIC107 to know about the connection and its memory allocation. Certainembodiments use VI connections provided by the Giganet driver. TheGiganet NIC driver code establishes a Virtual Interface pair (i.e., VI)and assigns it to a corresponding virtual interface id.

Each VI is a bi-directional connection established between one Giganetport and another, or more precisely between memory buffers and memoryqueues on one node to buffers and queues on another. The allocation ofports and memory is handled by the NIC drivers as stated above. Data istransmitted by placing it into a buffer the NIC knows about andtriggering action by writing to a specific memory-mapped register. Onthe receiving side, the data appears in a buffer and completion statusappears in a queue. The data never need be copied if the sending andreceiving programs are capable of producing and consuming messages inthe connection's buffers. The transmission can even be direct fromapplication program to application program if the operating systemmemory-maps the connection's buffers and control registers intoapplication address space. Each Giganet port can support 1024simultaneous VI connections over it and keep them separate from eachother with hardware protection, so the operating system as well asdisparate applications can safely share a single port. Under oneembodiment of the invention, 14 VI connections may be establishedsimultaneously from every port to every other port.

In preferred embodiments, the NIC drivers establish VI connections inredundant pairs, with one connection of the pair going through one ofthe two switch fabrics 115 a,b and the other through the other switch.Moreover, in preferred embodiments, data is sent alternately on the twolegs of the pair, equalizing load on the switches. Alternatively, theredundant pairs may be used in fail-over manner.

All the connection pairs established by the node persist as long as theoperating system remains up. Establishment of a connection pair tosimulate an Ethernet connection is intended to be analogous to, and aspersistent as, physically plugging in a cable between network interfacecards. If a node's defined configuration changes while its operatingsystem is running, then applicable redundant Virtual Interfaceconnection pairs will be established or discarded at the time of thechange.

The Giganet driver logic 325 on the control node-side operatesanalogously to the above.

Virtual LAN Server

The virtual LAN server logic 335 facilitates the emulation of anEthernet network over the underlying NBMA network. The virtual LANserver logic

-   -   1. manages membership to a corresponding virtual LAN;    -   2. provides RVI mapping and management;    -   3. ARP processing and IP mapping to RVI;    -   4. provides broadcast and multicast services;    -   5. facilitates bridging and routing to other domains; and    -   6. manages service clusters.

1. Virtual LAN Membership Management

Administrators configure the virtual LANs using management application135. Assignment and configuration of IP addresses on virtual LANs maydone in the same way as on an “ordinary” subnet. The choice of IPaddresses to use is dependent on the external visibility of nodes on avirtual LAN. If the virtual LAN is not globally visible (either notvisible outside the platform 100, or from the Internet), private IPaddresses should be used. Otherwise, IP addresses must be configuredfrom the range provided by the internet service provider (ISP) thatprovides the Internet connectivity. In general, virtual LAN IP addressassignment must be treated the same as normal LAN IP address assignment.Configuration files stored on the local disks of the control node 120define the IP addresses within a virtual LAN. For the purposes of avirtual network interface, an IP alias just creates another IP to RVImapping on the virtual LAN server logic 335. Each processor mayconfigure multiple virtual interfaces as needed. The primaryrestrictions on the creation and configuration of virtual networkinterfaces are IP address allocation and configuration.

Each virtual LAN has a corresponding instance of server logic 335 thatexecutes on both of the control nodes 120 and a number of nodesexecuting on the processor nodes 105. The topology is defined by theadministrator.

Each virtual LAN server 335 is configured to manage exactly onebroadcast domain, and any number of layer 3 (IP) subnets may be presenton the given layer 2 broadcast domain. The servers 335 are configuredand created in response to administrator commands to create virtualLANs.

When a processor 106 boots and configures its virtual networks, itconnects to the virtual LAN server 335 via a special management RVI. Theprocessors then obtain their data link configuration information, suchas the virtual MAC addresses assigned to it, virtual LAN membershipinformation and the like. The virtual LAN server 335 will determine andconfirm that the processor attempting to connect to it is properly amember of the virtual LAN that that server 335 is servicing. If theprocessor is not a virtual LAN member, the connection to the server isrejected. If it is a member, the virtual network driver 310 registersits IP address with the virtual LAN server. (The IP address is providedby the IP stack 305 when the driver 310 is configured.) The virtual LANserver then binds that IP address to an RVI on which the registrationarrived. This enables the virtual LAN server to find the processorassociated with a specific IP address. Additionally, the association ofIP addresses with a processor can be performed via the virtual LANmanagement interface 135. The latter method is necessary to properlyconfigure cluster IP addresses or IP addresses with special handling,discussed below.

2. RVI Mapping and Management

As outlined above, certain embodiments use RVIs to connect nodes at thedata link layer and to form control connections. Some of theseconnections are created and assigned as part of control nodes bootingand initialization. The data link layer connections are used for thereasons described above. The control connections are used to exchangemanagement, configuration, and health information.

Some RVI connections are between nodes for unicast traffic, e.g., 212₁₋₂. Other RVI connections are to the virtual LAN server logic 335 sothat the server can handle the requests, e.g., ARP traffic, broadcasts,and so on. To create the RVI the virtual LAN server 335 creates andremoves RVIs through calls to a Giganet switch manager 360 (providedwith the switch fabric and Giganet NICs). The switch manager may executeon the control nodes 120 and cooperates with the Giganet drivers tocreate the RVIs.

With regard to processor connections, as nodes register with the virtualLAN server 335, the virtual LAN server creates and assigns virtual MACaddresses for the nodes, as described above. In conjunction with this,the virtual LAN server logic maintains data structures reflecting thetopology and MAC assignments for the various nodes. The virtual LANserver logic then creates corresponding RVIs for the unicast pathsbetween nodes. These RVIs are subsequently allocated and made known tothe nodes during the nodes booting. Moreover, the RVIs are alsoassociated with IP addresses during the virtual LAN server's handling ofARP traffic. The RVI connections are torn down if a node is removed fromthe topology.

If a node 106 at one end of an established RVI connection is rebooted,the two operating systems of the each end of the connection, and RVImanagement logic re-establish the connection. Software using theconnection on the processing node that remained up will be unaware thatanything happened to the connection itself. Whether or not the softwarenotices or cares that the software at the other end was rebooted dependsupon what it is using the connection for and the extent to which therebooted end is able to re-establish its state from persistent storage.For example, any software communicating via Transmission ControlProtocol (TCP) will notice that all TCP sessions are closed by a reboot.On the other hand, Network File System (NFS) access is stateless and notaffected by a reboot if it occurs within an allowed timeout period.

Should a node be unable to send a packet on a direct RVI at any time, itcan always attempt to send the packet to a destination via the virtualLAN server 335. Since the virtual LAN server 335 is connected to allvirtual Ethernet driver 310 interfaces on the virtual LAN via thecontrol connections, virtual LAN server 335 can also serve as the packetrelay mechanism of last resort.

With regard to the connections to the virtual LAN server 335, certainembodiments use virtual Ethernet drivers 310 that algorithmicallydetermine the RVI that it ought to use to connect to its associatedvirtual LAN server 335. The algorithm, depending on the embodiment, mayneed to consider identification information such as cabinet number toidentify the RVI.

3. ARP Processing and IP Mapping to RVIs

As explained above, the virtual Ethernet drivers 310 of certainembodiments support ARP. In these embodiments, ARP processing is used toadvantage to create mappings at the nodes between IP addresses and RVIsthat may be used to carry unicast traffic, including IP packets, betweennodes.

To do this, the virtual Ethernet drivers 310 send ARP packet requestsand replies to the virtual LAN server 335 via a dedicated RVI. Thevirtual LAN server 335, and specifically ARP server logic 355, handlesthe packets by adding information to the packet header. As was explainedabove, this information facilitates identification of the source andtarget and identifies the RVI that may be used between the nodes.

The ARP server logic 355 receives the ARP requests, processes the TLVheader, and broadcasts the request to all relevant nodes on the internalplatform and the external network if appropriate. Among other things,the server logic 355 determines who should receive the ARP reply,resulting from the request. For example, if the source is a clustered IPaddress, the reply should be sent to the cluster load balancer, notnecessarily the source of the ARP request. The server logic 355indicates such by including information in the TLV header of the ARPrequest, so that the target of the ARP replies accordingly. The server335 will process the ARP packet by including further information in theappended header and broadcast the packet to the nodes in the relevantdomain. For example, the modified header may include informationidentifying the source cabinet, processing node number, RVI connectionnumber, channel, virtual interface number, and virtual LAN name (some ofwhich is only known by the server 335).

The ARP replies are received by the server logic 355, which then mapsthe MAC information in the reply to corresponding RVI relatedinformation. The RVI-related information is placed in the target MACentry of the reply and sent to the appropriate source node (e.g., may bethe sender of the request, but in some instances such as with clusteredIP addresses may be a different node).

4. Broadcast and Multicast Services

As outlined above, broadcasts are handled by receiving the packet on adedicated RVI. The packet is then cloned by the server 335 and unicastto all virtual interfaces 310 in the relevant broadcast domain.

The same approach may be used for multicast. All multicast packets willbe reflected off the virtual LAN server. Under some alternativeembodiments, the virtual LAN server will treat multicast the same asbroadcast and rely on IP filtering on each node to filter out unwantedpackets.

When an application wishes to send or receive multicast addresses itmust first join a multicast group. When a process on a processorperforms a multicast join, the processor virtual network driver 310sends a join request to the virtual LAN server 335 via a dedicated RVI.The virtual LAN server then configures a specific multicast MAC addresson the interface and informs the LAN Proxy 340, discussed below, asnecessary. The Proxy 340 will have to keep track of use counts onspecific multicast groups so a multicast address is only removed when noprocessor belongs to that multicast group.

5. Bridging and Routing to Other Domains

From the perspective of system 100, the external network 125 may operatein one of two modes: filtered or unfiltered. In filtered mode a singleMAC address for the entire system is used for all outgoing packets. Thishides the virtual MAC addresses of a processing node 107 behind theVirtual LAN Proxy 340 and makes the system appear as a single node onthe network 125 (or as multiple nodes behind a bridge or proxy). Becausethis doesn't expose unique link layer information for each internal node107 some other unique identifier is required to properly deliverincoming packets. When running in filter mode, the destination IPaddress of each incoming packet is used to uniquely identify theintended recipient since the MAC address will only identify the system.In unfiltered mode the virtual MACs of a node 107 are visible outsidethe system so that they may be used to direct incoming traffic. That is,filtered mode mandates layer 3 switching while unfiltered mode allowslayer 2 switching. Filtered mode requires that some component (in thiscase the Virtual LAN Proxy 340) perform replacement of node virtual MACaddresses with the MAC address of the external network 125 on alloutgoing packets.

Some embodiments support the ability for a virtual LAN to be connectedto external networks. Consequently, the virtual LAN will have to handleIP addresses not configured locally. To address this, one embodimentimposes a limit that each virtual LAN so connected be restricted to oneexternal broadcast domain. IP addresses and subnet assignments for theinternal nodes of the virtual LAN will have to be in accordance with theexternal domain.

The virtual LAN server 335 services the external connection byeffectively acting as a data link layer bridge in that it moves packetsbetween the external Ethernet driver 345 and internal processors andperforms no IP processing. However, unlike like a data link layerbridge, the server cannot always rely on distinctive layer two addressesfrom the external network to internal nodes and instead the connectionmay use layer 3 (IP) information to make the bridging decisions. To dothis, the external connection software extracts IP address informationfrom incoming packets and it uses this information to identify thecorrect node 106 so that it may move the packet to that node.

A virtual LAN server 335 having an attached external broadcast domainhas to intercept and process packets from and to the external domain sothat external nodes have a consistent view of the subnet(s) in thebroadcast domain.

When virtual LAN server 335 having an attached external broadcast domainreceives an ARP request from an external node it will relay the requestto all internal nodes. The correct node will then compose the reply andsend the reply back to the requestor through the virtual LAN server 335.The virtual LAN server cooperates with the virtual LAN Proxy 340 so thatthe Proxy may handle any necessary MAC address translation on outgoingrequests. All ARP Replies and ARP advertisements from external sourceswill be relayed directly to the target nodes.

Virtual Ethernet interfaces 310 will send all unicast packets with anexternal destination to the virtual LAN server 335 over the controlconnection RVI. (External destinations may be recognized by the driverby the MAC address format.) The virtual LAN server will then move thepacket to the external network 125 accordingly.

If the virtual LAN server 335 receives a broadcast or multicast packetfrom an internal node it relays the packet to the external network inaddition to relaying the packet to all internal virtual LAN members. Ifthe virtual LAN server 335 receives a broadcast or multicast packet froman external source it relays the packet to all attached internal nodes.

Under certain embodiments, interconnecting virtual LANs through the useof IP routers or firewalls is accomplished using analogous mechanisms tothose used in interconnecting physical LANs. One processor is configuredon both LANs, and the Linux kernel on that processor must have routing(and possibly IP masquerading) enabled. Normal IP subnetting and routingsemantics will always be maintained, even for two nodes located in thesame platform.

A processor could be configured as a router between two externalsubnets, between and external and internal subnet, and between twointernal subnets. When an internal node is sending a packet through arouter there are no problems because of the point-to-point topology ofthe internal network. The sender will send directly to the router (i.e.,processor so configured with routing logic) without the intervention ofthe virtual LAN server (i.e., typical processor to processorcommunication, discussed above).

When an external node sends a packet to an internal router, and theexternal network 125 is running in filtered mode, the destination MACaddress of the incoming packet will be that of the platform 100. Thusthe MAC address can not be used to uniquely identify the packetdestination node. For a packet whose destination is an internal node onthe virtual LAN, the destination IP address in the IP header is used todirect the packet to the proper destination node. However, becauserouters are not final destinations, the destination IP address in the IPheader is that of the final destination rather than that of the next hop(which is the internal router). Thus, there is nothing in the incomingpacket that can be used to direct it to the correct internal node. Tohandle this situation, one embodiment imposes a limit of no more thanone router exposed to an external network on a virtual LAN. This routeris registered with the virtual LAN server 335 as a default destinationso that incoming packets with no valid destination will be directed tothis default node.

When an external node sends a packet to an internal router and theexternal network 125 is running in unfiltered mode, the destination MACaddress of the incoming packet will be the virtual MAC address of theinternal destination node. The LAN Server 335 will then use this virtualMAC to send the packet directly to the destination internal node. Inthis case any number of internal nodes may be functioning as routers asthe incoming packet's MAC address will uniquely identify the destinationnode.

If a configuration requires multiple routers on a subnet, one router canbe picked as the exposed router. This router in turn could route to theother routers as necessary.

Under certain embodiments, router redundancy is provided, by making arouter a clustered service and load balancing or failing over on astateless basis (i.e., every IP packet rather than per-TCP connection).

Certain embodiments of the invention support promiscuous modefunctionality by providing switch semantics in which a given port may bedesignated as a promiscuous port so that all traffic passing through theswitch is repeated on the promiscuous port. The nodes that are allowedto listen in promiscuous mode will be assigned administratively at thevirtual LAN server.

When a virtual Ethernet interface 310 enters promiscuous receive mode itwill send a message to the virtual LAN server 335 over the managementRVI. This message will contain all the information about the virtualEthernet interface 310 entering promiscuous mode. When the virtual LANServer receives a promiscuous mode message from a node, it will checkits configuration information to determine if the node is allowed tolisten promiscuously. If not, the virtual LAN Server will drop thepromiscuous mode message without further processing. If the node isallowed to enter promiscuous mode, the virtual LAN server will broadcastthe promiscuous mode message to all other nodes on the virtual LAN. Thevirtual LAN server will also mark the node as being promiscuous so thatit can forward copies of incoming external packets to it. When apromiscuous listener detects any change in its RVI configuration it willsend a promiscuous mode message to the virtual LAN to update the stateof all other nodes on the relevant broadcast domain. This will updateany nodes entering or leaving a virtual LAN. When a virtual Ethernetinterface 310 leaves promiscuous it will send the virtual LAN server amessage informing it that the interface is leaving promiscuous mode. Thevirtual LAN server will then send this message to all other nodes on thevirtual LAN. Promiscuous settings will allow for placing an externalconnection in promiscuous mode when any internal virtual interface is apromiscuous listener. This will make the traffic external to theplatform (but on the same virtual LAN) available to the promiscuouslistener.

6. Managing Service Clusters

A service cluster is a set of services available at one or more IPaddress (or host names). Examples of these services are HTTP, FTP,telnet, NFS, etc. An IP address and port number pair represents aspecific service type (though not a service instance) offered by thecluster to clients, including clients on the external network 125.

FIG. 5 shows how certain embodiments present a virtual cluster 405 ofservices as a single virtual host to the Internet or other externalnetwork 125 via a cluster IP address. All the services of the cluster505 are addressed through a single IP address, through different portsat that IP address. In the example of FIG. 5, service B is a loadbalanced service.

With reference to FIG. 3B, virtual clusters are supported by theinclusion of virtual cluster proxy (VCP) logic 360 which cooperates withthe virtual LAN server 335. In short, VCP 360 is responsible forhandling distribution of incoming connections, port filters, and realserver connections for each configured virtual IP address. There will beone VCP for each clustered IP address configured.

When a packet arrives on the virtual cluster IP address, the virtual LANProxy logic 340 will send the packet to the VCP 360 for processing. TheVCP will then decide where to send the packet based on the packetcontents, its internal connection state cache, any load balancingalgorithms being applied to incoming traffic, and the availability ofconfigured services. The VCP will relay incoming packets based on boththe destination IP address as well as the TCP or UDP port number.Further, it will only distribute packets destined for port numbers knownto the VCP (or for existing TCP connections). It is the configuration ofthese ports, and the mapping of the port number to one or moreprocessors that creates the virtual cluster and makes specific serviceinstances available in the cluster. If multiple instances of the sameservice from multiple application processors are configured then the VCPcan load balance between the service instances.

The VCP 360 maintains a cache of all active connections that exist onthe cluster's IP address. Any load balancing decisions that are madewill only be made when a new connection is established between theclient and a service. Once the connection has been set up, the VCP willuse the source and destination information in the incoming packet headerto make sure all packets in a TCP stream get routed to the sameprocessor 106 configured to provide the service. In the absence of theability to determine a client session (for example, HTTP sessions), theactual connection/load balancing mapping cache will route packets basedon client address so that subsequent connections from the same clientgoes to the same processor (making a client session persistent or“sticky”). Session persistence should be selectable on a service portnumber basis since only certain types of services require sessionpersistence.

Replies to ARP requests, and routing of ARP replies, is handled by theVCP. When a processor sends any ARP packet, it will send it out throughthe Virtual Ethernet driver 310. The packet will then be sent to thevirtual LAN Server 335 for normal ARP processing. The virtual LAN serverwill broadcast the packet as usual, but will make sure it doesn't getbroadcast to any member of the cluster (not just the sender). It willalso place information in the packet header TLV that indicates to theARP target that the ARP source can only be reached through the virtualLAN server and specifically through the load balancer. The ARP target,whether internal or external, will process the ARP request normally andsend a reply back through the virtual LAN server. Because the source ofthe ARP was a cluster IP address, the virtual LAN server will be unableto determine which processor sent out the original request. Thus, thevirtual LAN Server will send the reply to each cluster member so thatthey can handle it properly. When an ARP packet is sent by a source witha cluster IP address as the target, the virtual LAN server will send therequest to every cluster member. Each cluster member will receive theARP request and process it normally. They will then compose an ARP replyand send it back to the source via the virtual LAN server. When thevirtual LAN server receives any ARP reply from a cluster member it willdrop that reply, but the virtual LAN server will compose and send an ARPreply to the ARP source. Thus, the virtual LAN Server will respond toall ARPs of the cluster IP address. The ARP reply will contain theinformation necessary for the ARP source to send all packets for thecluster IP address to the VCP. For external ARP sources, this willsimply be an ARP reply with the external MAC address as the sourcehardware address. For internal ARP sources this will be the informationnecessary to tell the source to send packets for the cluster IP addressdown the virtual LAN management RVI rather than through a directlyconnected RVI. Any gratuitous ARP packets that are received will beforwarded to all cluster members. Any gratuitous ARP packets sent by acluster member will be sent normally.

Virtual LAN Proxy

The virtual LAN Proxy 340 performs the basic co-ordination of thephysical network resources among all the processors that have virtualinterfaces to the external physical network 125. It bridges virtual LANserver 335 to the external network 125. When the external network 125 isrunning in filtered mode the Virtual LAN Proxy 340 will convert theinternal virtual MAC addresses from each node to the single external MACassigned to the system 100. When the external network 125 is operatingin unfiltered mode no such MAC translation is required. The Virtual LANProxy 340 also performs insertion and removal of IEEE 802.1Q Virtual LANID tagging information, and demultiplexing packets based on their VLANIds. It also serializes access to the physical Ethernet interface 129and co-ordinates the allocation and removal of MAC addresses, such asmulticast addresses, on the physical network.

When the external network 125 is running in filtered mode and thevirtual LAN Proxy 340 receives outgoing packets (ARP or otherwise) froma virtual LAN server 335, it replace the internal format MAC addresswith the MAC address of the physical Ethernet device 129 as the sourceMAC address. When the External Network 125 is running in unfiltered modeno such replacement is required.

When the virtual LAN Proxy 340 receives incoming ARP packets, it movesthe packet to the virtual LAN server 335 which handles the packet andrelays the packet on to the correct destination(s). If the ARP packet isa broadcast packet then the packet is relayed to all internal nodes onthe Virtual LAN. If the packet is a unicast packet the packet is sentonly to the destination node. The destination node is determined by theIP address in the ARP packet when the External Network 125 is running infiltered mode, or by the MAC address in the Ethernet header of the ARPpacket (not the MAC address is the ARP packet).

Physical LAN Driver

Under certain embodiments, the connection to the external network 125 isvia Gigabit or 100/10baseT Ethernet links connected to the control node.Physical LAN drivers 345 are responsible for interfacing with suchlinks. Packets being sent on the interface will be queued to the devicein the normal manner, including placing the packets in socket buffers.The queue used to queue the packets is the one used by the protocolstack to queue packets to the device's transmit routine. For incomingpackets, the socket buffer containing the packets will be passed aroundand the packet data will never be copied (though it will be cloned ifneeded for multicast operations). Under these embodiments, generic Linuxnetwork device drivers may be used in the control node withoutmodification. This facilitates the addition of new devices to theplatform without requiring additional device driver work.

The physical network interface 345 is in communication only with thevirtual LAN proxy 340. This prevents the control node from using theexternal connection in any way that would interfere with the operationof the virtual LANs and improves security and isolation of user data,i.e., an administrator may not “sniff” any user's packets.

Load Balancing and Failover

Under some embodiments, the redundant connections to the externalnetwork 125 will be used alternately to load balance packet transmissionbetween two redundant interfaces to the external network 125. Otherembodiments load balance by configuring each virtual network interfaceon alternating control nodes so the virtual interfaces are evenlydistributed between the two control nodes. Another embodiment transmitsthrough one control node and receives through another.

When in filtered mode, there will be one externally visible MAC addressto which external nodes transmit packets for a set of virtual networkinterfaces. If that adapter goes down, then not only do the virtualnetwork interfaces have to fail over to the other control node, but theMAC address must fail over too so that external nodes can continue tosend packets to the MAC address already in the ARP caches. Under oneembodiment of the invention, when a failed control node recovers, asingle MAC address is manipulated and the MAC address does not have tobe remapped on recovery.

Under another embodiment of the invention, load balancing is performedby allowing transmission on both control nodes but only receptionthrough one. The failover case is both send and receive through the samecontrol node. The recovery case is transmission through the recoveredcontrol node since that doesn't require any MAC manipulation.

The control node doing reception has IP information for filtering andmulticast address information for multicast MAC configuration. Thisinformation is needed to process incoming packets and should be failedover should the receiving control node fail. If the transmitting controlnode fails, virtual network drivers need only start sending outgoingpackets only to the receiving control node. No special failoverprocessing is required other than the recognition that the transmittingcontrol node has failed. If the failed control node recovers the virtualnetwork drivers can resume sending outgoing packets to the recoveredcontrol nodes without any additional special recovery processing. If thereceiving control node fails then the transmitting control node mustassume the receiving interface role. To do this, it must configure allMAC addresses on its physical interface to enable packet reception.Alternately, both control nodes could have the same MAC addressconfigured on their interfaces, but receives could be physicallydisabled on the Ethernet device by the device driver until an controlnode is ready to receive packets. Then failover would simply enablereceives on the device.

Because the interfaces must be configured with multicast MAC addresseswhen any processor has joined a multicast group, multicast informationmust be shared between control nodes so that failover will betransparent to the processor. Since the virtual network drivers willhave to keep track of multicast group membership anyway, thisinformation will always be available to a LAN Proxy via the virtual LANserver when needed. Thus, a receive failover will result in multicastgroup membership being queried from virtual network drivers to rebuildthe local multicast group membership tables. This operations is lowoverhead and requires no special processing except during failover andrecovery, and doesn't require any special replication of data betweencontrol nodes. When receive has failed over and the failed control noderecovers, only transmissions will be moved over to the recovered controlnode. Thus, the algorithm for recovery on virtual network interfaces isto always move transmissions to the recovered control node and leavereceive processing where it is.

Virtual service clusters may also use load balancing and failover.

Multicabinet Platforms

Some embodiments allow cabinets to be connected together to form largerplatforms. Each cabinet will have at least one control node which willbe used for inter-cabinet connections. Each control node will include avirtual LAN server 335 to handle local connections and traffic. One ofthe servers is configured to be a master, such as the one located on thecontrol node with the external connection for the virtual LAN. The othervirtual LAN server will act as proxy servers, or slaves, so that thelocal processors of those cabinets can participate. The master maintainsall virtual LAN state and control while the proxies relay packetsbetween the processors and masters.

Each virtual LAN server proxy maintains a RVI to each master virtual LANServer. Each local processor will connect to the virtual LAN ServerProxy server just as if it were a master. When a processor connects andregisters an IP and MAC address, the proxy will register that IP and MACaddress with the master. This will cause the master to bind theaddresses to the RVI from the proxy. Thus, the master will contain RVIbindings for all internal nodes, but proxies will contain bindings onlyfor nodes in the same cabinet.

When an processor anywhere in a multicabinet virtual LAN sends anypacket to its virtual LAN server, the packet will be relayed to themaster for processing. The master will then do normal processing on thepacket. The master will relay packets to the proxies as necessary formulticast and broadcast. The master will also relay unicast packetsbased on the destination IP address of the unicast packet and registeredIP addresses on the proxies. Note that on the master, a proxy connectionlooks very much like a node with many configured IP addresses.

Networking Management Logic

During times when there is no operating system running on a processingnode, such as booting or kernel debugging, the node's serial consoletraffic and boot image requests are routed by switch driver code locatedin the processing node's kernel debugging software or BIOS to managementsoftware running on a control node (not shown). From there, the consoletraffic can again be accessed either from the high-speed externalnetwork 125 or through the control node's management ports. The bootimage requests can be satisfied from either the control node's localdisks or from partitions out on the external SAN 130. The control node120 is preferably booted and running normally before anything can bedone to an processing node. The control node is itself booted ordebugged from its management ports.

Some customers may wish to restrict booting and debugging of controllersto local access only, by plugging their management ports into an on-sitecomputer when needed. Others may choose to allow remote booting anddebugging by establishing a secure network segment for managementpurposes, suitably isolated from the Internet, into which to plug theirmanagement ports. Once a controller is booted and running normally, allother management functions for it and for the rest of the platform canbe accessed from the high-speed external network 125 as well as themanagement ports, if permitted by the administrator.

Serial console traffic to and from each processing node 105 is sent byan operating system kernel driver over the switch fabric 115 tomanagement software running on a control node 120. From there, anynode's console traffic can be accessed either from the normal,high-speed external network 125 or through either of the control node'smanagement ports.

Storage Architecture

Certain embodiments follow a SCSI model of storage. Each virtual PAN hasits own virtualized I/O space and issues SCSI commands and status withinsuch space. Logic at the control node translates or transforms theaddresses and commands as necessary from a PAN and transmits themaccordingly to the SAN 130 which services the commands. From theperspective of the SAN, the client is the platform 100 and the actualPANs that issued the commands are hidden and anonymous. Because the SANaddress space is virtualized, one PAN operating on the platform 100 mayhave device numbering starting with a device number 1, and a second PANmay also have a device number 1. Yet each of the device number 1s willcorrespond to a different, unique portion of SAN storage.

Under preferred embodiments, an administrator can build virtual storage.Each of the PANs will have its own independent perspective of massstorage. Thus, as will be explained below, a first PAN may have a givendevice/LUN address map to a first location in the SAN, and a second PANmay have the same given device/LUN map to a second, different locationin the SAN. Each processor maps a device/LUN address into a major andminor device number, to identify a disk and a partition, for example.Though the major and minor device numbers are perceived as a physicaladdress by the PAN and the processors within a PAN, in effect they aretreated by the platform as a virtual address to the mass storageprovided by the SAN. That is, the major and minor device numbers of eachprocessor are mapped to corresponding SAN locations.

FIG. 6 illustrates the software components used to implement the storagearchitecture of certain embodiments. A configuration component 605,typically executed on a control node 120, is in communication withexternal SAN 130. A management interface component 610 provides aninterface to the configuration component 605 and is in communicationwith IP network 125 and thus with remote management logic 135 (see FIG.1). Each processor 106 in the system 100 includes an instance ofprocessor-side storage logic 620. Each such instance 620 communicatesvia 2 RVI connections 625 to a corresponding instance of controlnode-side storage logic 615.

In short, the configuration component 605 and interface 610 areresponsible for discovering those portions of SAN storage that areallocated to the platform 100 and for allowing an administrator tosuballocate portions to specific PANs or processors 106. Storageconfiguration logic 605 is also responsible for communicating the SANstorage allocations to control node-side logic 615. The processor-sidestorage logic 620 is responsible for communicating the processor'sstorage requests over the internal interconnect 110 and storage fabric115 via dedicated RVIs 625 to the control node-side logic 615. Therequests will contain, under certain embodiments, virtual storageaddresses and SCSI commands. The control node-side logic is responsiblefor receiving and handling such commands by identifying thecorresponding actual address for the SAN and converting the commands andprotocol to the appropriate form for the SAN, for example, including butnot limited to, fibre channel (Gigabit Ethernet with iSCSI is anotherexemplary connectivity).

Configuration Component

The configuration component 605 determines which elements in the SAN 130are visible to each individual processor 106. It provides a mappingfunction that translates the device numbers (e.g., SCSI target and LUN)that the processor uses into the device numbers visible to the controlnodes through their attached SCSI and Fibre Channel I/O interfaces 128.It also provides an access control function, which prevents processorsfrom accessing external storage devices which are attached to thecontrol nodes but not included in the processors' configuration. Themodel that is presented to the processor (and to the systemadministrator and applications/users on that processor) makes it appearas if each processor has its own mass storage devices attached tointerfaces on the processor.

Among other things, this functionality allows the software on aprocessor 106 to be moved to another processor easily. For example, incertain embodiments, the control node via software (without any physicalre-cabling) may change the PAN configurations to allow a new processorto access the required devices. Thus, a new processor may be made toinherit the storage personality of another.

Under certain embodiments, the control nodes appear as hosts on theSANs, though alternative embodiments allow the processors to act assuch.

As outlined above, the configuration logic discovers the SAN storageallocated to the platform 100 (for example, during platform boot) andthis pool is subsequently allocated by an administrator. If discovery isactivated later, the control node that performs the discovery operationcompares the new view with the prior view. Newly available storage isadded to the pool of storage that may be allocated by an administrator.Partitions that disappear that were not assigned are removed from theavailable pool of storage that may be allocated to PANs. Partitions thatdisappear that were assigned trigger error messages.

Management Interface Component

The configuration component 605 allows management software to access andupdate the information which describes the device mapping between thedevices visible to the control nodes 120 and the virtual devices visibleto the individual processors 106. It also allows access to controlinformation. The assignments may be identified by the processing node inconjunction with an identification of the simulated SCSI disks, e.g., byname of the simulated controller, cable, unit, or logical unit number(LUN).

Under certain embodiments the interface component 610 cooperates withthe configuration component to gather and monitor information andstatistics, such as:

-   -   Total number of I/O operations performed    -   Total number of bytes transferred    -   Total number of read operations performed    -   Total number of write operations performed    -   Total amount of time I/O was in progress

Processor-side Storage Logic

The processor-side logic 620 of the protocol is implemented as a hostadapter module that emulates a SCSI subsystem by providing a low-levelvirtual interface to in the operating system on the processors 106. Theprocessors 106 use this virtual interface to send SCSI I/O commands tothe control nodes 120 for processing.

Under embodiments employing redundant control nodes 120, each processingnode 105 will include one instance of logic 620 per control node 120.Under certain embodiments, the processors refer to storage usingphysical device numbering, rather than logical. That is, the address isspecified as a device name to identify the LUN, the SCSI target,channel, host adapter, and control node 120 (e.g., node 120 a or 120 b).As shown in FIG. 8, one embodiment maps the target (T) and LUN (L) to ahost adapter (H), channel (C), mapped target (mT), and mapped LUN (mL)

FIG. 7 shows an exemplary architecture for processor side logic 720.Logic 720 includes a device-type-specific driver (e.g., a disk driver)705, a mid-level SCSI I/O driver 710, and wrapper and interconnect logic715.

The device-type-specific driver 705 is a conventional driver providedwith the operating system and associated with specific device types.

The mid-level SCSI I/O driver 710 is a conventional mid-level driverthat is called by the device-type-specific driver 705 once the driver705 determines that the device is a SCSI device.

The wrapper and interconnect logic 715 is called by the mid-level SCSII/O driver 710. This logic provides the SCSI subsystem interface andthus emulates the SCSI subsystem. In certain embodiments that use theGiganet fabric, logic 715 is responsible for wrapping the SCSI commandsas necessary and for interacting with the Giganet and RCLAN interface tocause the NIC to send the packets to the control nodes via the dedicatedRVIs to the control nodes, described above. The header information forthe Giganet packet is modified to indicate that this is a storage packetand includes other information, described below in context. Though notshown in FIG. 7, wrapper logic 715 may use the RCLAN layer to supportand utilize redundant interconnects 110 and fabrics 115.

For embodiments that use Giganet fabric 115, the RVIs of connection 725are assigned virtual interface (VI) numbers from the range of 1024available VIs. For the two endpoints to communicate, the switch 115 isprogrammed with a bidirectional path between the pair (control nodeswitch port, control node VI number), (processor node 105 switch port,processor node VI number).

A separate RVI is used for each type of message sent in eitherdirection. Thus, there is always a receive buffer pending on each RVIfor a message that can be sent from the other side of the protocol. Inaddition, since only one type of message is sent in either direction oneach RVI, the receive buffers posted to each of the RVI channels can besized appropriately for the maximum message length that the protocolwill use for that type of message. Under other embodiments, all of thepossible message types are multiplexed onto a single RVI, rather thanusing 2 VIs. The protocol and the message format do not specificallyrequire the use of 2 RVIs, and the messages themselves have message typeinformation in their header so that they could be demultiplexed.

One of the two channels is used to exchange SCSI commands (CMD) andstatus (STAT) messages. The other channel is used to exchange buffer(BUF) and transmit (TRAN) messages. This channel is also used to handledata payloads of SCSI commands.

CMD messages contain control information, the SCSI command to beperformed, and the virtual addresses and sizes of I/O buffers in thenode 105. STAT messages contain control information and a completionstatus code reflecting any errors that may have occurred whileprocessing the SCSI command. BUF messages contain control informationand the virtual addresses and sizes of I/O buffers in the control node120. TRAN messages contain control information and are used to confirmsuccessful transmission of data from node 105 to the control node 120.

The processor side wrapper logic 715 examines the SCSI command to besent to determine if the command requires the transfer of data and, ifso, in what direction. Depending on the analysis, the wrapper logic 715sets appropriate flag information in the message header accordingly. Thesection describing the control node-side logic describes how the flaginformation is utilized.

Under certain embodiments of the invention, the link 725 betweenprocessor-side storage logic 720 and control node-side storage logic 715may be used to convey control messages, not part of the SCSI protocoland not to be communicated to the SAN 130. Instead, these controlmessages are to be handled by the control node-side logic 715.

The protocol control messages are always generated by the processor-sideof the protocol and sent to the control node-side of the protocol overone of two virtual interfaces (VIs) connecting the processor-side logic720 to the control node-side storage logic 715. The message header usedfor protocol control operations is the same as a command message header,except that different flag bits are used to distinguish the message as aprotocol control message. The control node 120 performs the requestedoperation and responds over the RVI with a message header that is thesame as is used by a status message. In this fashion, a separate RVI forthe infrequently used protocol control operations is not needed.

Under certain embodiments using redundant control nodes, theprocessor-side logic 720 detects certain errors from issued commands andin response re-issues the command to the other control node. This retrymay be implemented in a midlevel driver 710.

Control Node-side Storage Logic

Under certain embodiments, the control node-side storage logic 715 isimplemented as a device driver module. The logic 715 provides adevice-level interface to the operating system on the control nodes 120.This device-level interface is also used to access the configurationcomponent 705. When this device driver module is initialized, itresponds to protocol messages from all of the processors 106 in theplatform 100. All of the configuration activity is introduced throughthe device-level interface. All of the I/O activity is introducedthrough messages that are sent and received through the interconnect 110and switch fabric 115. On the control node 120, there will be oneinstance of logic 715 per processor node 105 (though it is only shown asone box in FIG. 7). Under certain embodiments, the control node-sidelogic 715 communicates with the SAN 130 via FCP or FCP-2 protocols, oriSCSI or other protocols that use the SCSI-2 or SCSI-3 command set overvarious media.

As described above, the processor-side logic sets flags in the RVImessage headers indicating whether data flow is associated with thecommand and, if so, in which direction. The control node-side storagelogic 715 receives messages from the processor-side logic and thenanalyzes the header information to determine how to act, e.g., toallocate buffers or the like. In addition, the logic translates theaddress information contained in the messages from the processor to thecorresponding, mapped SAN address and issues the commands (e.g., via FCPor FCP-2) to the SAN 130.

A SCSI command such as a TEST UNIT READY command, which does not requirea SCSI data transfer phase, is handled by the processor-side logic 720sending a single command on the RVI used for command messages, and bythe control node-side logic sending a single status message back overthe same RVI. More specifically, the processor-side of the protocolconstructs the message with a standard message header, a new sequencenumber for this command, the desired SCSI target and LUN, the SCSIcommand to be executed, and a list size of zero. The control node-sideof the logic receives the message, extracts the SCSI command informationand conveys it to the SAN 130 via interface 128. After the control nodehas received the command completion callback, it constructs a statusmessage to the processor using a standard message header, the sequencenumber for this command, the status of the completed command, andoptionally the request sense data if the command completed with a checkcondition status.

A SCSI command such as a READ command, which requires a SCSI datatransfer phase to transfer data from the SCSI device into the hostmemory, is handled by the processor-side logic sending a command messageto the control node-side logic 715, and the control node responding withone or more RDMA WRITE operation into memory in the processor node 105,and a single status message from the control node-side logic. Morespecifically, the processor-side logic 720 constructs a command messagewith a standard message header, a new sequence number for this command,the desired SCSI target and LUN, the SCSI command to be executed, and alist of regions of memory where the data from the command is to bestored. The control node-side logic 715 allocates temporary memorybuffers to store the data from the SCSI operation while the SCSI commandis executing on the control node. After the control node-side logic 715has sent the SCSI command to the SAN 130 for processing and the commandhas completed it sends the data back to the processor 105 memory with asequence of one or more RDMA WRITE operations. It then constructs astatus message with a standard message header, the sequence number forthis command, the status of the completed command, and optionally theREQUEST SENSE data if the command completed with a SCSI CHECK CONDITIONstatus.

A SCSI command such as a WRITE command, which requires a SCSI datatransfer phase to transfer data from the host memory to the SCSI device,is handled by the processor-side logic 720 sending a single commandmessage to the control node-side logic 715, one or more BUF messagesfrom the control node-side logic 715 to the processor-side logic, one ormore RDMA WRITE operations from the processor-side storage logic intomemory in the control node, one or more TRAN messages from theprocessor-side logic to the control node-side logic, and a single statusmessage from the control node-side logic back to the processor-sidelogic. The use of the BUF messages to communicate the location oftemporary buffer memory in the control node to the processor-sidestorage logic and the use of TRAN messages to indicate completion of theRDMA WRITE data transfer is due to the lack of RDMA READ capability inthe underlying Giganet fabric. If the underlying fabric supports RDMAREAD operations, a different sequence of corresponding actions may beemployed. More specifically, the processor-side logic 720 constructs aCMD message with a standard message header, a new sequence number forthis command, the desired SCSI target and LUN, and the SCSI command tobe executed. The control node-side logic 715 allocates temporary memorybuffers to store the data from the SCSI operation while the SCSI commandis executing on the control node. The control node-side of the protocolthen constructs a BUF message with a standard message header, thesequence number for this command, and a list of regions of virtualmemory which are used for the temporary memory buffers on the controlnode. The processor-side logic 720 then sends the data over to thecontrol node memory with a sequence of one or more RDMA WRITEoperations. It then constructs a TRAN message with a standard messageheader, and the sequence number for this command After the controlnode-side logic has sent the SCSI command to the SAN 130 for processingand has received the command completion, it constructs a STAT messagewith a standard message header, the sequence number for this command,the status of the completed command, and optionally the REQUEST SENSEdata if the command completed with a CHECK CONDITION status.

Under some embodiments, the CMD message contains a list of regions ofvirtual memory from where the data for the command is stored. The BUFand TRAN messages also contain an index field, which allows the controlnode-side of the protocol to send a separate BUF message for each entryin the region list in the CMD message. The processor-side of theprotocol would respond to such a message by performing RDMA WRITEoperations for the amount of data described in the BUF message, followedby a TRAN message to indicate the completion of a single segment of datatransfer.

The protocol between the processor-side logic 720 and the controlnode-side logic 715 allows for scatter-gather I/O operations. Thisfunctionality allows the data involved in an I/O request to be read fromor written to several distinct regions of virtual and/or physicalmemory. This allows multiple, non-contiguous buffers to be used for therequest on the control node.

As stated above, the configuration logic 705 is responsible fordiscovering the SAN storage allocated to the platform and forinteracting with the interface logic 710 so that an administrator maysuballocate the storage to specific PANs. As part of this allocation,the configuration component 705 creates and maintains a storage datastructure 915 that includes information identifying the correspondencebetween processor addresses and actual SAN addresses. FIG. 7 shows sucha structure. The correspondence, as described above, may be between theprocessing node and the identification of the simulated SCSI disks,e.g., by name of the simulated controller, cable, unit, or logical unitnumber (LUN).

Management Logic

Management logic 135 is used to interface to control node software toprovision the PANs. Among other things, the logic 135 allows anadministrator to establish the virtual network topology of a PAN, itsvisibility to the external network (e.g., as a service cluster), and toestablish the types of devices on the PAN, e.g., bridges and routing.

The logic 135 also interfaces with the storage management interfacelogic 710 so that an administrator may define the storage for a PANduring initial allocation or subsequently. The configuration definitionincludes the storage correspondence (SCSI to SAN) discussed above andaccess control permissions.

As described above, each of the PANs and each of the processors willhave a personality defined by its virtual networking (including avirtual MAC address) and virtual storage. The structures that recordsuch personality may be accessed by management logic, as describedbelow, to implement processor clustering. In addition, they may beaccessed by an administrator as described above or with an agentadministrator. An agent for example may be used to re-configure a PAN inresponse to certain events, such as time of day or year, or in responseto certain loads on the system.

The operating system software at a processor includes serial consoledriver code to route console I/O traffic for the node over the Giganetswitch 115 to management software running on a control node. From there,the management software can make any node's console I/O streamaccessible via the control node's management ports (its low-speedEthernet port and its Emergency Management Port) or via the high-speedexternal network 125, as permitted by an administrator. Console trafficcan be logged for audit and history purposes.

Cluster Management Logic

FIG. 9 illustrates the cluster management logic of certain embodiments.The cluster management logic 905 accesses the data structures 910 thatrecord the networking information described above, such as the networktopologies of PANs, the MAC address assignments within a PAN and so on.In addition, the cluster management logic 905 accesses the datastructures 915 that record the storage correspondence of the variousprocessors 106. Moreover, the cluster management logic 905 accesses adata structure 920 that records free resources such as unallocatedprocessors within the platform 100.

In response to processor error events or administrator commands, thecluster management logic 905 can change the data structures to cause thestorage and networking personalities of a given processor to “migrate”to a new processor. In this fashion, the new processor “inherits” thepersonality of the former processor. The cluster management logic 905may be caused to do this to swap a new processor in to a PAN to replacea failing one.

The new processor will inherit the MAC address of a former processor andact like the former. The control node will communicate the connectivityinformation when the new processor boots, and will update theconnectivity information for the non-failing processors as needed. Forexample, in certain embodiments, the RVI connections for the otherprocessors are updated transparently; that is, the software on the otherprocessors does not need to be involved in establishing connectivity tothe newly swapped in processor. Moreover, the new processor will inheritthe storage correspondence of the former and consequently inherit thepersisted state of the former processor.

Among other advantages this allows a free pool of resources, includingprocessors, to be shared across the entire platform rather than acrossgiven PANs. In this way, the free resources (which may be kept as suchto improve reliability and fault tolerance of the system) may be usedmore efficiently.

When a new processor is “swapped in” it will need to re-ARP to learn IPaddress to MAC address associations.

Alternatives

As each Giganet port of the switch fabric 115 can support 1024simultaneous Virtual Interface connections over it and keep themseparate from each other with hardware protection, the operating systemcan safely share a node's Giganet ports with application programs. Thiswould allow direct connection between application programs without theneed to run through the full stack of driver code. To do this, anoperating system call would establish a Virtual Interface channel andmemory-map its buffers and queues into application address space. Inaddition, a library to encapsulate the low-level details of interfacingto the channel would facilitate use of such Virtual Interfaceconnections. The library could also automatically establish redundantVirtual Interface channel pairs and manage sharing or failing overbetween them, without requiring any effort or awareness from the callingapplication.

The embodiments described above emulated Ethernet internally over anATM-like fabric. The design may be changed to use an internal Ethernetfabric which would simplify much of the architecture, e.g., obviatingthe need for emulation features. If the external network communicatesaccording to ATM, another variation would use ATM internally withoutemulation of Ethernet and the ATM could be communicated externally tothe external network when so addressed. Another variation would allowATM internally to the platform (i.e., without emulation of Ethernet) andonly external communications are transformed to Ethernet. This wouldstreamline internal communications but require emulation logic at thecontroller.

Certain embodiments deploy PANs based on software configurationcommands. It will be appreciated that deployment may be based onprogrammatic control. For example, more processors may be deployed undersoftware control during peak hours of operation for that PAN, orcorresponding more or less storage space for a PAN may be deployed undersoftware algorithmic control.

It will be appreciated that the scope of the present invention is notlimited to the above described embodiments, but rather is defined by theappended claims; and that these claims will encompass modifications ofand improvements to what has been described.

1. A method of implementing the address resolution protocol (ARP) in acomputing platform having a plurality of processors interconnected by anon-Ethernet physical network, comprising: defining a topology of anEthernet network to be emulated on the computing platform, the topologyincluding processor nodes and a switch node; assigning a set ofprocessors from the plurality to be processors to act as the processornodes; assigning a processor to act as the switch node and to emulate anEthernet switch; allocating virtual interfaces for the underlyingnon-Ethernet physical network, the virtual interfaces providing directsoftware communication paths between two processors connected to thenon-Ethernet physical network, wherein each virtual interface has acorresponding identification; a first processor node, in response toneeding to communicate an IP packet to a target IP node for which thefirst processor node has an IP address but insufficient, correspondinglower layer address information, communicating an ARP request to theswitch node via the non-Ethernet physical network, wherein the ARPrequest includes an LP address for the target node; the switch nodecommunicating, via the non-Ethernet physical network, the ARP request toall other processor nodes in the emulated Ethernet network; a secondprocessor node that is assigned the IP address for the target IP nodereceiving the ARP request and issuing an ARP reply in response; thesecond processor node having its ARP table programmed to associate theIP address of the first node with a corresponding virtual interface forthe underlying non-Ethernet physical network; the first processorreceiving and processing the ARP reply; the first processor node havingits ARP table programmed to associate the IP address of the target IPnode with a corresponding virtual interface for the underlyingnon-Ethernet physical network; wherein for subsequent unicast IPcommunication between the first and second nodes, the first and secondprocessor nodes respectively use their ARP tables and the virtualinterfaces associated therewith to communicate directly betweenprocessor nodes over the non-Ethernet physical network, avoiding theswitch node; and wherein a subset of the processors are organized as acluster and wherein one of the processors in the cluster is a loadbalancing processor node, and wherein, when any processor in the clusterissues an ARP request, the ARP request is programmed to include a MACaddress for the load balancing processor node rather than for therequesting node, so that the reply to the ARP request is sent to theload balancing processor node rather than to the requesting node, andwhen the load balancing node receives the ARP reply it distributes saidreply to all nodes in the cluster.
 2. The method of claim 1 wherein theunderlying physical network is a point-to-point mesh connecting theplurality of processors.
 3. The method of claim 1 wherein the switchnode is in communication with an external IP network, and wherein theact of communicating an ARP reply includes identifying that the ARPreply is from a processor node in the platform.
 4. The method of claim 1wherein the second processor node includes driver logic to modify theARP request to include virtual interface information so that the ARPtable of the second processor node associates the IP address of thefirst node with virtual interface information for the first processornode.
 5. The method of claim 1 wherein the first processor node includesdriver logic to modify the ARP reply to include virtual interfaceinformation so that the ARP table of the first processor node associatesthe IP address of the second node with virtual interface information forthe second processor node.
 6. An address resolution protocol (ARP)system, comprising: a computing platform having a plurality ofprocessors connected by an underlying non-Ethernet physical network;logic, executable on one of the processors, to define a topology of anEthernet network to be emulated on the computing platform, the topologyincluding processor nodes and a switch node; logic, executable on one ofthe processors, to assign a set of processors from the plurality to beprocessors to act as the processor nodes; logic, executable on one ofthe processors, to allocate virtual interfaces for the underlyingnon-Ethernet physical network to provide direct software communicationpaths between two processors connected to the non-Ethernet physicalnetwork, wherein each virtual interface has a correspondingidentification; each processor node having ARP request logic tocommunicate an ARP request to the switch node, wherein the ARP requestincludes an IP address; the switch node including ARP request broadcastlogic to communicate via the non-Ethernet physical network the ARPrequest to all other processor nodes in the emulated Ethernet network;each processor node having ARP reply logic to determine whether it isthe processor node associated with the IP address in an ARP request and,if so, to issue an ARP reply, and having logic to program its ARP tableto associate the IP address of the ARP requester with a correspondingvirtual interface for the underlying non-Ethernet physical network; eachprocessor node further having logic, responsive to ARP replies, toprogram its ARP table to associate the IP address of the ARP replierwith a corresponding virtual interface for the underlying non-Ethernetphysical network; wherein for subsequent unicast IP communicationbetween the first and second nodes, the first and second processor nodesrespectively use their ARP tables and the virtual interfaces associatedtherewith to communicate directly between processor nodes over thenon-Ethernet physical network, avoiding the switch node; and wherein asubset of the processors are organized as a cluster and wherein one ofthe processors in the cluster is a load balancing processor node, andwherein, when any processor in the cluster issues an ARP request, theARP request is programmed to include a MAC address for the loadbalancing processor node rather than for the requesting node, so thatthe reply to the ARP request is sent to the load balancing processornode rather than to the requesting node, and when the load balancingnode receives the ARP reply it distributes said reply to all nodes inthe cluster.
 7. The system of claim 6 wherein the underlying physicalnetwork is a point-to-point mesh connecting the plurality of processors.8. The system of claim 6 wherein the switch node is in communicationwith an external IP network, and wherein the processor node ARP replylogic includes logic to identify that the ARP reply is from a processornode in the platform.
 9. A method of implementing the address resolutionprotocol (ARP) in a computing platform having a plurality of processorsinterconnected by a non-Ethernet physical network, comprising: defininga topology of an Ethernet network to be emulated on the computingplatform, the topology including processor nodes and a switch node;assigning a set of processors from the plurality to be processors to actas the processor nodes; assigning a processor to act as the switch nodeand to emulate an Ethernet switch so that the switch nodes and processornodes form an emulated Ethernet network; allocating virtual interfacesfor the underlying non-Ethernet physical network, the virtual interfacesproviding direct software communication paths between two processorsconnected to the non-Ethernet physical network, wherein each processornode has corresponding virtual interface address information and saidcorresponding virtual interface address information is specified in MACaddress format and has a predefined setting of select address bits toidentify the MAC address as carrying virtual interface addressinformation within the MAC address format; a first processor node, inresponse to needing to communicate an IP packet to a target IP node forwhich the first processor node has an IP address but insufficient,corresponding lower layer address information, communicating an ARPrequest to the switch node via the non-Ethernet physical network,wherein the ARP request includes an IP address for the target node; theswitch node communicating, via the non-Ethernet physical network, theARP request to all other processor nodes in the emulated Ethernetnetwork; a second processor node that is assigned the IP address for thetarget IP node receiving the ARP request and issuing an ARP reply inresponse; the second processor node having its ARP table programmed toassociate the IP address of the first node with its correspondingvirtual interface address information specified in MAC address format;the first processor receiving and processing the ARP reply; the firstprocessor node having its ARP table programmed to associate the IPaddress of the target IP node with its corresponding virtual interfaceaddress information specified in MAC address format.
 10. An addressresolution protocol (ARP) system, comprising: a computing platformhaving a plurality of processors connected by an underlying non-Ethernetphysical network; logic, executable on one of the processors, to definea topology of an Ethernet network to be emulated on the computingplatform, the topology including processor nodes and a switch node;logic, executable on one of the processors, to assign a set ofprocessors from the plurality to be processors to act as the processornodes; logic, executable on one of the processors, to allocate virtualinterfaces for the underlying non-Ethernet physical network to providedirect software communication paths between two processors connected tothe non-Ethernet physical network, wherein each processor node hascorresponding virtual interface address information and saidcorresponding virtual interface address information is specified in MACaddress format and has a predefined setting of select address bits toidentify the MAC address as carrying virtual interface addressinformation within the MAC address format; each processor node havingARP request logic to communicate an ARP request to the switch node,wherein the ARP request includes an IP address; the switch nodeincluding ARP request broadcast logic to communicate via thenon-Ethernet physical network the ARP request to all other processornodes in the emulated Ethernet network; each processor node having ARPreply logic to determine whether it is the processor node associatedwith the IP address in an ARP request and, if so, to issue an ARP reply,and having logic to program its ARP table to associate the IP address ofthe ARP requester with its corresponding virtual interface addressinformation specified in MAC address format; each processor node furtherhaving logic, responsive to ARP replies, to program its ARP table toassociate the IF address of the ARP replier with its correspondingvirtual interface address information specified in MAC address format;wherein for subsequent unicast IF communication between the first andsecond nodes, the first and second processor nodes respectively usetheir ARP tables and the virtual interfaces associated therewith tocommunicate directly between processor nodes over the non-Ethernetphysical network, avoiding the switch node.